The levels and status of calcium and phosphate ions in saliva are clearly of importance in the equilibria which exist between the dental enamel and the saliva, in the processes leading to the formation of carious lesions and their remineralization and in the events leading to calculus formation. Saliva is a metastable solution with respect to basic calcium phosphate such as the enamel mineral and could, therefore be an efficient source of calcium and phosphate in the oral environment. However, saliva contains non-ultrafiltrable substances which inhibit hydrolysis of dicalcium phosphate, dihydrate and retard calcium phosphate precipitation when saliva is seeded with hydroxyapatite and interfere with apatite formation from calcium, phosphate and fluoride. That such inhibitors are probably also present in plaque is suggested by high concentrations of calcium and phosphate in the aqueous phase of plaque, by the observation that dicalcium phosphate is the earliest mineral identified in plaque and by preservation of this mineral even in old calculus. The purpose of the proposed research is to identify, isolate and characterize salivary inhibitors of hydrolysis of dicalcium phosphates and formation of apatite and, further, to assay saliva for inhibitors of apatite formation from fluoride-calcium-phosphate interaction. It is also proposed to determine the extent of inhibition of apatite formation and dicalcium phosphate hydrolysis in plaque. Finally, it is proposed to evaluate, in pilot studies, the clinical role of inhibitory substances. The findings will provide information on the remineralizing capacity of saliva and the interaction of salivary calcium and phosphate with fluoride. Similar data on plaque and identification of the inhibitors which prevent basic calcium phosphate formation will lead to a better understanding of the processes of demineralization and remineralization occurring in carious lesions.